The introduction of low-cost microprocessors has been one impetus in the push towards distributed processing. Almost all such microprocessors have the capability and the standard interfaces to be interconnected into distributed processing systems. In such systems, processors may be installed at remote sites near where processing is needed, and intercommunication among processors is usually done utilizing serial transmission techniques.
When a processor is utilized to communicate with a plurality of peripheral units on a common data link, this processor must have some type of collision avoidance protocol associated therewith. This is especially true when the common data link is a wireless transmission system. One example is a processor/peripheral unit interface over a wireless data link which utilizes remotely disposed memories that can be accessed from a centrally disposed location. This type of system usually incorporates a number of different memories which are portable, with each memory having the ability to be interfaced with a central processor at the centralized location through the wireless data link that is shared with the other remote memories. Each of these memories therefore must be protected with some type of gating or arbitration circuit that can recognize the presence of a transmission directed toward the associated memory. It is difficult to specifically direct information to any one of the remote memories since they may move in and out of the transmission range. This is to be compared with hard wired systems, such as token ring passing systems, etc., that utilize identification codes or positions on the ring to determine the destination of a predetermined packet of data. However, most of the hard wired systems require that the ID be associated with the particular module disposed at the remote location. With these types of systems, this is easily done, as they are generally at fixed locations.
In systems where wireless transmission is utilized and remote stations can be mobile, it is virtually impossible to determine at the centralized location what remote locations are in the transmission range of the centralized location. Unless a predetermined protocol is provided wherein two-way communication is allowed, the centralized location has little information as to which remote devices or memories are in the transmission range. It merely transmits the information out with a particular ID and waits for some type of response indicating receipt of the information. However, present systems do not allow for polling of the devices on a minimal overhead basis.